[$] Better hugetlb page-table walking

The kernel must often step through the page tables of one or more processes
to carry out various operations. This 'page-table walking' tends to be
performed by ad-hoc (duplicated) code all over the kernel. Oscar Salvador
used a memory-management-track session at the 2025 Linux Storage,
Filesystem, Memory-Management, and BPF Summit to talk about strategies to
unify the kernel's page-table walking code just a little bit by making
hugetlb pages look more like ordinary pages.